Many organic compounds such as dyes, polymers and natural products can be damaged or destroyed either by the direct absorption of ultraviolet light, or by the action of free radicals produced by the absorption of ultraviolet light. One method of protecting such materials is by overcoating or imbibing the material to be protected with an ultraviolet light ("UV") absorber. A UV absorber is a material which is capable of absorbing radiation in the range of about 250-400 nm and dissipating the absorbed energy while undergoing little or no destruction itself. Although there is a great need for such materials, there are only a very few classes that have been found to possess the required stability. These are the O-hydroxyphenyl benzotriazoles, the O-hydroxybenzophenones, the phenysalicylates, and certain butadiene and arylidene materials containing both donor and acceptor substituents.
Photographic elements in particular have specific requirements for a UV absorber. Typical photographic elements use silver halide emulsions, the silver halide having a native sensitivity to ultraviolet UV radiation ("UV"). Such UV sensitivity is usually undesirable in that it produces an image on the photographic element which is not visible to the human eye. In addition, in the case of color photographic elements, in particular, color dye images formed on the light sensitive emulsion layers by color development easily undergo fading or discoloration due to the action of UV. Also, color formers, or so-called couplers, remaining in the emulsion layers are subject to the action of UV to form undesirable color stains on the finished photographs. The fading and the discoloration of the color images are easily caused by UV of wavelengths near the visible region, namely, those of wavelengths from 300 to 400 nm. For the foregoing reasons, photographic elements typically incorporate a UV absorbing material in an upper layer. The O-hydroxyphenylbenzotriazole class of UV absorbers has been particularly useful for photographic purposes since the spectrum of each covers a broad region of the UV but is still sharp cutting on the long wavelength side near 400 nm.
Given the very few classes of compounds which are suitable as UV absorbers, it is desirable to have new classes of UV absorbers particularly for application in photographic elements, which UV absorbers possess good photostability and high molecular extinction coefficients, so that less material is used to give the same amount of absorption.